In recent years there has been an increasing development of studies and experimentation in the field of engines of the type specified above. The present applicant is the holder of numerous patents and patent applications regarding a system for variable actuation of the valves, in which each variable-actuation valve is governed by the respective cam by means of a tappet and corresponding hydraulic means, which include a fluid chamber that is connectable by means of an electronically controlled solenoid valve with an exhaust channel, for the purpose of decoupling the valve itself from the respective tappet and causing rapid closing of the valve as a result of the respective means of elastic return. The solenoid valves that control communication of the fluid chambers associated to the various variable-actuation valves of the engine are controlled electronically according to different possible strategies, as the operating conditions of the engine vary, to achieve advantages in terms of performance and/or efficiency of operation of the engine, and/or reduction of fuel consumption, and/or reduction of harmful exhaust emissions.
Examples of known systems are described and illustrated in the European patents Nos. EP 1 273 770 B1 and EP 1 321 634 B1 filed in the name of the present applicant.
Even though the present invention is particularly aimed at an electro-hydraulic system of the type illustrated in the aforesaid prior documents, it is, however, applicable in general to any type of system of variable actuation of the valves of an engine, i.e., to any system that will enable modification of the times of opening and closing of the valve and the valve lift as the operating conditions of the engine vary. There have, for instance, been proposed in the last few years also systems of an electromechanical type for variable actuation of the valves, in which each valve is governed by a cam of the engine camshaft by means of an electronically controlled variable mechanical transmission, or also electromagnetic or electro-hydraulic valve-actuation systems without cams (“camless” systems). As has been said, the principles of the present invention are applicable also to systems of these kinds or to any other system for variable actuation of the valves, it being able to perform the valve motions described in the present invention.